1. Technical Field
The present invention relates generally to information processing and, in particular, to a fully decoupled LC tank based oscillator topology for low phase noise and high oscillation amplitude applications.
2. Description of the Related Art
Oscillator phase noise is a key performance metric in many wireless and wireline communication applications, radars, sensors, imagers, data converters, and so forth. Any clocked system performance would benefit from a lower noise oscillator. One way to lower oscillator phase noise is to increase the amplitude of oscillation. Within a given technology, the maximum amplitude is determined by the breakdown of the active devices (FETs, BJTs or other types of devices). Oscillator phase noise can also be lowered by using lower noise devices or higher breakdown devices, by lowering the temperature, and so forth.
A general expression for oscillator noise is given by Leeson's formula as follows:
      L    ⁡          (      Δω      )        =      10    ⁢                  ⁢    log    ⁢          {                                    2            ⁢            FkT                                P            sig                          ⁢                  (                      1            +                                          (                                                      ω                    0                                                        2                    ⁢                    Q                    ⁢                                                                                  ⁢                    Δω                                                  )                            2                                )                    }      
From this equation we see that at a given temperature T, frequency of oscillation ω0, offset from the carrier Δω and Q factor, the only way to decrease phase noise is to increase the signal power (Psig) (or, equivalently, the amplitude of the oscillation), keeping the noise factor, F, constant. Here k=1.3806503×10−23 m2 kg/s2/K is the Boltzmann constant.
Within a given technology increasing the amplitude to noise ratio is the most direct practical approach to solving this fundamental problem. It is important to emphasize that in general a lower noise active device also has a lower breakdown voltage. Additionally, in virtually all technologies, the breakdown voltage of the active devices is much lower than the breakdown voltage of passive devices. Note also that the breakdown of some passive devices (such as Metal-Oxide-Metal capacitors) can be controlled to a certain extent by design.